Polybenzoxazole membranes prepared from aromatic polyamide membranes

Abstract

The present invention discloses high performance polybenzoxazole membranes prepared from aromatic poly(o-hydroxy amide) membranes by thermal cyclization and a method for using these membranes. The polybenzoxazole membranes were prepared by thermal treating aromatic poly(o-hydroxy amide) membranes in a temperature range of 200° to 550° C. under inert atmosphere. The aromatic poly(o-hydroxy amide) membranes used for making the polybenzoxazole membranes were prepared from aromatic poly(o-hydroxy amide) polymers comprising pendent phenolic hydroxyl groups ortho to the amide nitrogen in the polymer backbone. In some embodiments of the invention, the polybenzoxazole membranes may be subjected to an additional crosslinking step to increase the selectivity of the membranes. These polybenzoxazole membranes showed significantly improved permeability for gas separations compared to the precursor aromatic poly(o-hydroxy amide) membranes and are not only suitable for a variety of liquid, gas, and vapor separations, but also can be used in catalysis and fuel cells.

1 . A process for separating one gas or liquid from a mixture of gases or liquids comprising providing a polybenzoxazole membrane prepared from an aromatic poly(o-hydroxy amide) membrane that is permeable to one gas or liquid; contacting the mixture of gases or liquids on one side of the polybenzoxazole membrane to cause one gas or liquid to permeate the polybenzoxazole membrane; and removing from the opposite side of the membrane a permeate gas or liquid composition that is a portion of said one gas or liquid which permeated the membrane. 
     
     
         2 . The process of  claim 1  wherein said separation is selected from the group consisting of desalination of water by reverse osmosis, non-aqueous liquid separation, ethanol/water separations, pervaporation dehydration of aqueous/organic mixtures, CO 2 /CH 4 , CO 2 /N 2 , H 2 /CH 4 , O 2 /N 2 , H 2 S/CH 4 , olefin/paraffin, and iso/normal paraffins separations. 
     
     
         3 . The process of  claim 1  wherein said polybenzoxazole membrane is made by subjecting an aromatic poly(o-hydroxy amide) membrane prepared from an aromatic poly(o-hydroxy amide) polymer to thermal cyclization in a temperature range of from about 200° to 550° C. under an inert atmosphere. 
     
     
         4 . The process of  claim 3  wherein said polybenzoxazole membrane has been crosslinked. 
     
     
         5 . The process of  claim 4  wherein said crosslinking is by UV crosslinking of the polybenzoxazole membrane wherein said polybenzoxazole membrane comprises UV crosslinkable functional groups. 
     
     
         6 . The process of  claim 1  wherein said polybenzoxazole membrane comprises repeating units of a formula (I), wherein said formula (I) is represented by: 
       
         
           
           
               
               
           
         
       
       where 
       
         
           
           
               
               
           
         
       
       is selected from the group consisting of 
       
         
           
           
               
               
           
         
       
       and mixtures thereof, —R— is selected from the group consisting of 
       
         
           
           
               
               
           
         
       
       and mixtures thereof, and 
       
         
           
           
               
               
           
         
       
       is selected from the group consisting of 
       
         
           
           
               
               
           
         
       
       and mixtures thereof. 
     
     
         7 . The process of  claim 1  wherein said poly(o-hydroxy amide) polymer comprises a plurality of first repeating units of a formula (II), wherein formula (II) is: 
       
         
           
           
               
               
           
         
       
       where 
       
         
           
           
               
               
           
         
       
       is selected from the group consisting of 
       
         
           
           
               
               
           
         
       
       and mixtures thereof, —R— is selected from the group consisting of 
       
         
           
           
               
               
           
         
       
       and mixtures thereof, and 
       
         
           
           
               
               
           
         
       
       is selected from the group consisting of 
       
         
           
           
               
               
           
         
       
       and mixtures thereof. 
     
     
         8 . The process of  claim 1  wherein said 
       
         
           
           
               
               
           
         
       
       of formula (II) is selected from the group consisting of 
       
         
           
           
               
               
           
         
       
       and mixtures thereof and wherein —R— group is represented by the formula: 
       
         
           
           
               
               
           
         
       
     
     
         9 . The process of  claim 1  wherein 
       
         
           
           
               
               
           
         
       
       of formula (II) is selected from the group consisting of 
       
         
           
           
               
               
           
         
       
       and mixtures thereof. 
     
     
         10 . The process of  claim 1  wherein said polyamide polymer comprises 
       
         
           
           
               
               
           
         
       
       where n is an integer ranging from 15 to 500. 
     
     
         11 . The process of  claim 1  wherein said polyamide polymer comprises 
       
         
           
           
               
               
           
         
       
       where n is an integer ranging from 15 to 500. 
     
     
         12 . The process of  claim 1  wherein said polyamide polymer comprises 
       
         
           
           
               
               
           
         
       
       where n is an integer ranging from 15 to 500. 
     
     
         13 . The process of  claim 1  wherein a selective layer surface of said polybenzoxazole membrane is coated with a thin layer of a material selected from the group consisting of a polysiloxane, a fluoro-polymer, a thermally curable silicone rubber or a UV radiation curable epoxy silicone. 
     
     
         14 . The process of  claim 1  wherein said polybenzoxazole membrane is in a geometry selected from the group consisting of flat sheet, spiral wound, disk, tube, hollow fiber, and thin film composite.